A Chirally Locked Bis-perylene Diimide Macrocycle: Consequences for Chiral Self-Assembly and Circularly Polarized Luminescence

Temperature and Solvent Dual Switch Photochromic Chiral Ionic Hydrogen-Bonded Organic Framework for Circularly Polarized Luminescence and Advanced Encryption

Multi-response encryption materials with temperature control and time resolution have attracted widespread attention due to their unique response characteristics and higher application security. The design and development of photochromic crystalline materials with multiple stimulus responses remain challenging. In this study, we report a pair of responsive photochromic chiral ionic hydrogen-bonded organic framework (iHOF) R/S-iHOF-19, controlled by both temperature and solvent through charge-assisted synthesis. The chromophore tetrakis(4-sulfophenyl)ethylene (H4TPE) acts as an electron donor and (1R/S,2R/S)-1,2-diphenylethylenediamine (R/S-DPEN) as an electron acceptor and chiral source. Water and methanol molecules connect the donor and acceptor and interact to build a 3D supramolecular framework. Notably, water and methanol molecules form independent hydrogen-bonding channels within the iHOF structural framework, providing a transfer path for the photoinduced electrons. Surprisingly, the formation of a continuous chiral supramolecular framework by R/S-DPEN while generating photo-induced radicals under ultraviolet (UV) irradiation at -20 °C imparts excellent circularly polarized luminescence (CPL) properties to R/S-iHOF-19. The glum values reach -1.8 × 10-3 and +3.75 × 10-3, respectively, and show an enhancement of the circular polarization of light with decreasing temperature. This CPL with unique low-temperature stimulus-responsive photochromism provides new guidance and perspectives for the development of information security and multiple encryption materials.

Synthesis of Alternatively-Twisted Nanographenes by Semi-Deprotection-Induced Cyclization

Twisted nanographenes (NGs) are currently attracting a lot of attention owing to their geometrical and electronic structures that differ substantively from conventional planar and nonplanar NGs, while the strategic synthesis of twisted NGs is still a topic of interest because the products are often interconvertible among unidirectionally, alternatively, or randomly twisted geometries and otherwise obtained as a mixture of them. Herein, we report the conformationally specific synthesis of twisted NGs where the geometry was reinforced by introducing 1,4-dioxane rings at a K-region of a central pyrene core that bears a large contortion. The 1,4-dioxane rings were generated by semi-deprotection, of tetraoxa[4.4.4]-propellanes in precursor molecules, which were confirmed to be engaged in forming C-C bonds via a Friedel-Crafts type mechanism. The large contortion within the pyrene core causes a narrowed HOMO-LUMO gap on account of unusual p z -lobe overlap between +z and -z sides, giving rise to red emission with a high quantum yield of 94% as well as stable redox processes of 2e- uptake/release.

Chiral nanographenes exhibiting circularly polarized luminescence

Chiral nanographenes constitute an unconventional material class that deviates from planar graphene cutouts. They have gained considerable attention for their ability to exhibit circularly polarized luminescence (CPL), which offers new opportunities in chiral optoelectronics. Their unique π-conjugated architectures, coupled with the ability to introduce chirality at the molecular level, have made them powerful contenders in developing next-generation optoelectronic devices. This review thoroughly explores recent advances in the synthesis, structural design, and CPL performance of chiral nanographenes. We delve into diverse strategies for inducing chirality, including covalent functionalization, helically twisted frameworks, and heteroatom doping, each of which unlocks distinct CPL behaviors. In addition, we discuss the mechanistic principles governing CPL and future directions in chiral nanographenes to achieve high dissymmetry factors (glum) and tunable emission properties. We also discuss the key challenges in this evolving field, including designing robust chiral frameworks, optimizing CPL efficiency, and scaling up real-world applications. Through this review, we aim to shed light on recent developments in the bottom-up synthesis of structurally precise chiral nanographenes and evaluate their impact on the growing domain of circularly polarized luminescent materials.

Core-Twisted, Cationic Perylene Diimides; Homochiral Dimerization and Chiroptical Anion Sensing

Core-twisted perylene diimides (PDIs) are chiral organic dyes that may be exploited for self-assembled chiroptical materials or for the enantioselective recognition and sensing of chiral substrates. Discrete self-assembled dimers and host-guest complexes of core-twisted perylene diimides are important for furthering our understanding of this supramolecular chemistry, yet they are rare because the twisted perylene core significantly weakens intermolecular π-π interactions with the PDI's π-surface. To address this challenge, we have installed hydrogen bond donor groups in the PDI's bay positions, which direct the formation of a robust, co-facial and homochiral intermolecular PDI dimer. The structure of this discrete dimer is distinct from previous aggregates of non-planar PDIs that utilize the imide position for hydrogen bonding. We also uncover the potential of core-twisted, dicationic PDIs for the enantioselective recognition and chiroptical sensing of chiral anions and investigate the basis of this response via chiral complementarity in the discrete host-guest complex.

Chiral co-assembly of a polyoxometalate complex with an achiral pyrene derivative enables redox-modulated circularly polarized luminescence

We report the fabrication of helical structures with responsive circularly polarized lumunescence (CPL) via the chiral co-assembly of a cholesterol-modified Lindqvist type polyoxometalate (POM) and an achiral pyrenyl derivative. The chiral surfactant encapsulated POM (CSEP) complex was synthesized by combining (TBA)2[Mo6O19] with cholesterol-containing organic surfactants through ion exchange. It was found that the CSEP complex self-assembled into left-handed helical structures in mixed organic solvents, which could serve as a chiral template that enables achiral pyrenyl fluorophores (Py) to exhibit chiroptical properties. When doping Py at a ratio of 5 wt% into the system, the chiral co-assembly with CSEP in the mixed organic solvent results in the formation of helical nanofibers, which emit blue CPL signals. Furthermore, the chiral helical structures can be dynamically transformed to spherical aggregates upon UV illumination, accompanied by photochromism. The disappearance of CPL signals corresponded to the disruption of the chiral morphology in the co-assembled nanostructures. More importantly, the morphology transformation is reversible. The nanospheres transform into helical nanofibers under the oxidation of H2O2, which could trigger the regeneration of CPL signals. This work contributes to the understanding and development of chiral supramolecular systems featuring stimulus-responsive CPL switches.

A Bis-Perylene Diimide Macrocycle Chiroptical Switch

Helical assemblies of organic dyes are ubiquitous chiral organic materials, with valuable properties including chiroptical switching due to the dynamic nature of supramolecular chirality. Herein, we report a novel chiral bis-perylene diimide macrocycle, which acts as a discrete molecular model for a chiral supramolecular assembly. Point chirality is installed through amino acid-derived imide groups which, upon macrocyclization, is translated into helical chirality in the perylene diimide dimer. In solution, the macrocycle's chiroptical properties are switchable, with both the sign (+/-) and amplitude (on/off) of the signal tuned using solvent and molecular recognition stimuli respectively. The chiral structure-property relationships identified from this macrocycle are important for the design of high fidelity supramolecular chiroptical switches.

Rigidly Locked Pyrene Excimers in Planar Chiral Pyrenophanes for Intense and Stable Circularly Polarized Photoluminescence and Electrochemiluminescence

Aiming at the construction of novel platforms with excellent performances in both circularly polarized photoluminescence (CP-PL) and electrochemiluminescence (CP-ECL), a new family of pyrenophanes with rigidly locked pyrene dimers and varied bridges has been designed and synthesized. Attributed to densely packed pyrene excimers, the resultant pyrenophanes revealed tunable bridge-dependent emission behaviors, as investigated by femtosecond time-resolved transient absorption spectroscopy. More importantly, all these planar chiral pyrenophanes display strong CP-PL with large dissymmetry factor (gPL) values up to 0.034, and such excellent performances remain stable in a wide range of solvents, temperatures, and concentrations. Attractively, the highest gECL values up to 0.014 reported so far has been achieved for the CP-ECL emissions of the chiral pyrenophanes. Attributed to their unique structural features and outstanding CPL performances, these novel pyrenophanes could serve as promising platforms for both fundamental investigations on pyrene excimers and practical applications such as chiral sensing.

Advances in Chiral Macrocycles: Molecular Design and Applications

Chiral macrocycles have recently emerged as promising materials for enantioselective recognition, asymmetric catalysis, and circularly polarized luminescence (CPL) due to their terminal-free structure, preorganized chiral cavities, and unique host-guest and self-assembly properties. This review summarizes recent advances in the design and synthesis of chiral macrocycles with central, axial, helical, and planar chirality, each imparting distinct structural and chiroptical characteristics. We highlight key strategies for constructing these macrocycles and their applications in optoelectronic and catalytic systems. Emphasis is placed on the balance between rigidity and flexibility in macrocycle design, essential for effective molecular recognition, adaptable catalysis, and CPL. We conclude with perspectives on future opportunities, anticipating ongoing developments in chiral macrocycle research.

Oxidation Triggered Supramolecular Chirality

Topochemical reactions normally occurring in the solid and crystalline state exhibit solvent-free and catalyst-free properties, with high atom economy properties, which have been widely applied in materials science and polymer synthesis. Herein, we explore the potential of topochemical reactions for controlling the emergence of supramolecular chirality and the precise fabrication of chiroptical materials. Boronic acid pinacol esters (BPin) were conjugated to naphthalimides containing an inherent chiral cholesteryl group linked by alkyl or benzene spacers. The BPin segments were oxidized by H2O2 to form hydroxyl groups, which enhanced luminescence, reduced steric effects, and increased amphiphilicity. The inherent liposomal aggregates underwent in situ oxidation and transformed into 1D nanoarchitectures, exhibiting macroscopic chirality, active Cotton effects, and circularly polarized luminescence. Oxidation could also initiate an intimate interplay between the building units and the guest molecule, by which the chirality and chiroptical evolution in the multiple component chiral assembly system were realized.

Chemical oxidation of a double-twisted nanographene

Chemical oxidation of a double-twisted nanographene led to quantitative generation of corresponding dicationic species, which exhibited an intense absorption band tailing to 1500 nm wherein two orthogonally arranged π-skeletons contributed to transitions and a high dissymmetry factor of -0.0209 was recorded at 1443 nm in the NIR-II region.

Concentration-Switchable Assembly of Carbon Dots for Circularly Polarized Luminescent Amplification in Chiral Logic Gates and Deep-Red Light-Emitting Diodes

Stimuli-responsive circularly polarized luminescent (CPL) materials are expected to find widespread application in advanced information technologies, such as 3D displays, multilevel encryption, and chiral optical devices. Here, using R-/S-α-phenylethylamine and 3,4,9,10-perylenetetracarboxylic dianhydride as precursors, chiral carbon dots (Ch-CDs) exhibiting bright concentration-dependent luminescence are synthesized, demonstrating reversible responses in both their morphologies and emission spectra. By adjusting Ch-CD concentration, the switchable wavelength is extended over 180 nm (539-720 nm), with the maximum quantum efficiency reaching 100%. Meanwhile, upon increasing Ch-CD concentration, the emission wavelength red-shifts, while the chirality of the assembled nanoribbons is synchronously amplified, ultimately achieving CPL at 709 nm and a maximum luminescence asymmetry factor of 2.18 × 10-2. These values represent the longest wavelength and the largest glum reported for CDs. Considering the remarkable optical properties of the synthesized Ch-CDs, multilevel chiral logic gates are designed, and their potential practical applications are demonstrated in multilevel anti-counterfeiting encryption, flexible electronic printing, and solid-state CPL. Furthermore, deep-red chiral electroluminescence light-emitting diodes (EL-LEDs) are prepared using these Ch-CDs, achieving an external quantum efficiency of 1.98%, which is the highest value reported to date for CDs in deep-red EL-LEDs, and the first report of chiral electronic devices based on CDs.

Ionic Hydrogen-Bonded Organic Frameworks with a Two-Photon Synergistic Color Change and Their Information Encryption Applications

Photochromic hydrogen-bonded organic frameworks (HOFs) can introduce different luminescent functional groups to achieve synergistic controlled multiple color change properties, which are in great demand for diverse information encryption applications. We report in this paper switchable photochromic and photoluminescent dual luminescent functional group HOFs constructed with synergistic effects by N,N'-bis(2-phenylalanine)-1,4,5,8-naphthalenediimine (H2PheNDI) and benzenecarboximidamide 4,4'-azobis(hydrochloride) (AZBH). The crystal powder of iHOF-41 is orange-red in color, which can be changed to black under the irradiation of a 365 nm ultraviolet (UV) light source for 15 min. The photoisomerization rate of the crystal solution under continuous UV irradiation for 5 h was close to 99%. The composite membranes can achieve the properties of photochromism and photoluminescence when they are discolored under 365 nm UV irradiation and, at the same time, excite red bright fluorescence. This work achieves the construction of HOFs based on switching biluminescent functional groups and explores the synergistic mechanism of the photoisomerization process and photochromism as well as its practical application in information encryption.

Twisted Nanographenes with Robust Conformational Stability

Owing to a lack of methodology for rationally and selectively synthesizing twisted nanographenes, it is usually inevitable that we obtain nanographenes as a mixture with various geometries, such as unidirectionally twisted, alternatively twisted, randomly twisted, and even wavy structures, reflecting the high activation barriers among them. Otherwise, they are interconvertible if the barriers are low enough such that only averaged properties can be observed under a thermal equilibrium. Recently, we reported on a double-twisted nanographene containing four [6]helicene units within the skeleton. In this paper, we discuss the robust conformational stability of the nanographene, both experimentally and computationally. The results indicate that the nanographene could only be racemized at temperatures exceeding 200 °C, and the first flip of one of the four [6]helicene units is the rate-degerming step.

Ultrafast and Coherent Dynamics in a Solvent Switchable "Pink Box" Perylene Diimide Dimer

Perylene diimide (PDI) dimers and higher aggregates are key components in organic molecular photonics and photovoltaic devices, supporting singlet fission and symmetry breaking charge separation. Detailed understanding of their excited states is thus important. This has proven challenging because interchromophoric coupling is a strong function of dimer architecture. Recently, a macrocyclic PDI dimer was reported in which excitonic coupling could be turned on and off simply by changing the solvent. This presents a useful case where coupling is modified without synthetic changes to tune supramolecular structure. Here we present a detailed study of solvent dependent excited state dynamics in this dimer by means of coherent multidimensional spectroscopy. Spectral analysis resolves the different coupling strengths, which are consistent with solvent dependent changes in dimer conformation. The strongly coupled conformer forms an excimer within 300 fs. The low-frequency Raman active modes recovered from two-dimensional electronic spectra reveal frequencies characteristic of exciton coupling. These are assigned to modes modulating the coupling from the corresponding DFT calculations. Further analysis reveals a time dependent frequency during excimer formation. Analysis of two-dimensional "beatmaps" reveals features in the coupled dimer which are not predicted by the displaced harmonic oscillator model and are assigned to vibronic coupling.

Perylene Diimide-Embedded Chiral Carbaporphyrin

Herein, we report the synthesis of a novel carbaporphyrin incorporating perylene diimide (PDI) and dipyrromethane units. The twisted plane of the PDI subunits imbues carbaporphyrin with intriguing conformational chirality and stable chiroptical properties. Both experimental and theoretical studies reveal that the unique properties arise from the rigidly conjugated macrocyclic architecture and the reduced interchromophoric distance. This work successfully integrates PDIs into carbaporphyrins, thereby expanding their structural diversity and functional potential.